Industrial ammunition

ABSTRACT

A projectileless ammunition system ( 20; 320 ) includes a metallic case ( 22; 322 ). A propellant charge ( 26; 326 ) is carried by the case and cover by an over-powder member ( 24; 324 ) in the absence of a separate projectile. The ammunition is advantageously used with an industrial ballistic tool operating so that each spent case serves as the effective projectile to be propelled by firing of the next round of ammunition.

CROSS-REFERENCE TO RELATED APPLICATION

This is the U.S. National Stage of PCT/US00/25866, entitled “INDUSTRIALAMMUNITION” filed Sep. 21, 2000 and published in English on Mar. 29,2001 as WO 01/22026 and claims priority to U.S. Provisional PatentApplication No. 60/155,052, entitled “INDUSTRIAL AMMUNITION AND METHODAND APPARATUS FOR USE THEREOF” filed Sep. 21, 1999.

BACKGROUND OF THE INVENTION

(1) Field of the Invention

This invention relates to industrial ballistic tools, and moreparticularly to ammunition therefor.

(2) Description of the Related Art

Industrial ballistic tools are used in a variety of applications. Onecommon application is the in situ cleaning of kilns, for which the toolsare commonly identified as kiln guns. Additional applications lie in thetapping and cleaning of furnaces, the cleaning of copper smelters, thecleaning and clearing of silos, the cleaning of boilers, and the like.

By way of example, rotary kilns, which are used to calcine cement andlime, are typically 3 to 7 meters in diameter and 30 to 150 meters long.Calcining takes place at elevated temperatures, typically in the rangeof 1100° C. to 1500° C. During the calcining process, because of manyprocessing variables, the product may adhere to the sidewall of the kilnforming a clinker, ring or dam. If this adherent obstruction is notremoved, additional product will accumulate, reducing or stoppingthroughput. Removal of the obstruction is necessary.

It is not economically feasible to stop the kiln to remove theobstruction. Also, considering that the ring may form 5 to 10 metersfrom the end of the kiln, it is not safe or efficient for an operator toattempt to manually remove the obstruction with a long pole or by likemethods. Thus many users of rotary kilns utilize industrial ballistictools. A tool operator will position the tool in a kiln port and thenfire metallic projectiles at the obstruction. Impact of the projectileswith the obstruction removes the obstruction from the sidewall of thekiln. The metallic projectiles are usually formed from lead, a densematerial with a relatively low vaporization (boiling) temperature of1750° C. The lead projectiles knock clinkers from the kiln sidewall andthen fall into the kiln and may be vaporized.

Industrial ballistic tools are also utilized by manufacturers of steel,ferrosilicon and other materials. Prior to casting these metals, moltenmetal is typically contained within an electric furnace sealed by acarbon or clay base plug. Since the molten metal is at a temperature inexcess of 2500° C., manual removal of the plug is not feasible. One waythat the plug may be removed is with an industrial ballistic tool. Ametallic projectile is fired from the industrial ballistic tool to breakopen the plug, starting the flow of molten metal. To preventcontamination of the metal, the projectile typically is formed of amaterial such as lead that will vaporize on contact with the moltenmetal after rupturing the plug.

Due to environmental concerns, lead is being phased out as a projectilematerial for use with industrial ballistic tools. Zinc and zinc alloyshave also been utilized as lead substitutes. Their relatively lowdensity may make them disadvantageous for certain uses. A ballisticallystabilized zinc-based projectile is described in U.S. Pat. No. 5,824,944of Jack D. Dippold et al.

Additionally, when repeated firing heats the tool chamber, the plastictubes of many existing industrial shells may melt and/or leave aresidue. The residue may deleteriously affect the firing of subsequentrounds.

In other fields, so-called “bulletless ammunition” has been developed.Cartridges without bullets or other substantial projectiles have beenutilized as “blanks” or to propel grenades and the like. However, U.S.Pat. No. 3,621,781 discloses bulletless ammunition in which the sidewallof a spent cartridge becomes the projectile propelled by the charge ofthe subsequent cartridge. In the small arms field, substantialdevelopments in such bulletless ammunition technology were made byDouglas Olson. These include use of cut down brass rifle cases as thecase/projectile for use in revolvers and autoloaders. These arediscussed in Karwan, C. Hollowpoinp Bulletless Ammo, Hi-Tech Firearms,Petersen Publishing Co., (October, 1998), pp. 65-68.

BRIEF SUMMARY OF THE INVENTION

Accordingly, in one aspect, the invention is directed to ammunition foruse with a discharging apparatus which has a chamber for receiving theammunition, a muzzle, and a barrel between the chamber and the muzzle.The ammunition includes a case comprising in major part zinc andextending aft-to-fore from a base to a mouth and having interior andexterior surfaces. A propellant charge is carried within the case. Anover-powder member cooperates with the case to enclose the propellantcharge. The ammunition lacks a projectile within the case in a locationeffective to be expelled from the apparatus and having a mass in excessof a mass of the case.

In various implementations, the case may be a unitary casting of a zincalloy. The case exterior surface may have at least eight circumferentialgrooves, the grooves occupying a total of at least about 25% of a lengthof the case. The plurality of grooves may have widths of between 0.9 mmand 1.8 mm, peak depths of between 0.08 mm and 0.30 mm from a maximumcase diameter and, along with interspersed ungrooved areas, extend alongat least 70% of the case length. The peak depths may be between 0.13 mmand 0.23 mm and the widths between 1.1 mm and 1.5 mm. The interspersedungrooved areas may have diameters within 0.05 mm of the maximum casediameter. The ammunition may be combined with an industrial ballistictool barrel having rifling with a land-to-land diameter which is0.943-0.950 in. (2.395-2.413 cm) and a groove-to-groove diameter whichis 0.954-0.960 in. (2.423-2.438 cm). The case exterior surface may havea circumferential extractor groove having a depth of at least 1 mm andseparated by no more than 2 mm from an aft extremity of the case. Theammunition may further include a primer. The primer may comprise ametallic cup mounted in the case base. The primer maybe a #209 primer.The case may have a mass of between 70 g and 10 g, a length of between50 mm and 65 mm, and a maximum diameter of between 20 mm and 26 mm. Theover-powder member may be a plug or it may be a cap which extends from arear rim to a front end and has a rear portion encircling a fore portionof the case. The cap may be formed of a resinous polymer. The case foreportion may include a flange having an external flange diameter. The caprear portion may include an inwardly directed part aft of the flange andhaving an external diameter less than the flange diameter so as tocooperate with the flange to resist forward translation of the caprelative to the flange. A cap length may be between 100% and 3000% of acase length. There may be a first radial clearance of at least 1.0 mmbetween the flange and the cap. There may be a second radial clearanceof between interference fit and 0.5 mm between the cap inwardly directedpart and a neck portion of the case aft of the flange.

In another aspect, the invention is directed to ammunition for use witha discharging apparatus including a chamber for receiving theammunition, a muzzle, and a barrel between the chamber and the muzzle.The ammunition extends from a rear end to a front end and includes ametallic case. The case extends aft-to-fore from a base at theammunition rear end to a mouth and has interior and exterior surfaces. Acover is formed of a polymeric resin and extends from a rear rim to afront end at the ammunition front end. The cover has a mass not inexcess of the mass of the case and has interior and exterior surfaces.The ammunition further includes a propellant charge advantageouslyconfined within at least one of the case and cover.

In various implementation, the case may have a central longitudinalchannel extending forward from the primer pocket at the base to a foreportion proximate the mouth. A primer may be mounted within the primerpocket. The propellant charge may be confined within a volume at leastpartially defined by the central longitudinal channel and the coverinterior surface. The cover may have a cover length and the case mayhave case length less than the cover length. The cover may consistessentially of injection molded high density polyethylene and the casemay consist essentially of die cast zinc or zinc alloy. The coverinterior surface may have a circumferential recess forward of the caseand effective to locally weaken the cover. The weakening is sufficientto permit internal pressure within the cover to sever a portion ahead ofthe recess from a portion behind which remains attached to the case whenthe ammunition is fired. The recess may have a longitudinal extent ofbetween 1 mm to 5 mm and may locally thin the cover to a minimumthickness of between 0.6 mm and 1.4 mm from an adjacent thickness ofbetween 1.6 mm and 2.6 mm. The case may have a mass of between 70 g and10 g, a length of between 30 mm and 40 mm, and a maximum diameter ofbetween 20 mm and 26 mm. The case exterior surface may have a pluralityof circumferential grooves, the grooves occupying a total of at leastabout 25% of a length of the case.

In another aspect, the invention is directed to a method for operatingan industrial ballistic tool to discharge a plurality of ammunitionrounds. A plurality of ammunition rounds are provided each comprising azinc case and a charge of propellant. A first such round is insertedinto a chamber of the tool. Ignition of the charge of the firstammunition round is caused. A second such ammunition round is insertedinto the chamber. Ignition of the charge of the second ammunition roundis caused so as to expel the spent case of the first ammunition roundout of the muzzle at an effective muzzle kinetic energy.

In various implementation of the invention, the second round insertionand ignition may be repeated, each time utilizing a new ammunition roundto expel the case of the previously-discharged round. Prior to insertionof the first round, a chargeless case may be inserted into the chamberso that the insertion of the first round advances the chargeless casetoward the muzzle. Prior to insertion of the first round, a preliminaryround may be inserted into the chamber. The charge of the preliminaryround may not be ignited and insertion of the first round advances thepreliminary round toward the muzzle. Alternatively, the charge of thepreliminary round may be ignited and insertion of the first roundadvances the spent case of the preliminary round toward the muzzle. Themuzzle kinetic energy may be at least 10 kJ. Insertion of the secondround may include engaging an aft end of the spent case of the firstround with a fore end of the second round so as to advance the spentcase toward the tool muzzle. The ignition of the charge of the secondammunition round may include permitting a first portion of anon-metallic cover portion of the second ammunition round to separatefrom a remaining second portion and travel behind the spent case of thefirst ammunition round. This may further comprise permitting theremaining second portion to seal against the chamber to resistcombustion gas leakage around the case of the second round.

The present invention may facilitate a number of advantages over priorart slugs. A key potential advantage is cost. Beyond manufacturing cost,costs of collection and disposal of spent hulls is eliminated. Anotheradvantage is that use of a metal case does not entail the meltingassociated with plastic tubes of conventional industrial ammunition.This may increase reliability.

The details of one or more embodiments of the invention are set forth inthe accompanying drawings and the description below. Other features,objects, and advantages of the invention will be apparent from thedescription and drawings, and from the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a longitudinal cross-sectional view of an ammunition roundaccording to principles of the invention.

FIG. 2 is a semi-schematic longitudinal sectional view of a spent roundin the chamber of an industrial ballistic tool.

FIG. 3 is a semi-schematic longitudinal cross-sectional view of a loadedround in the chamber of the tool with the spent round advanced tandemlyahead.

FIG. 4 shows the round and spent case of FIG. 3 shortly after the roundis fired.

FIG. 5 shows the round and spent case of FIG. 4 as the spent caseadvances down the tool barrel.

FIG. 6 is a longitudinal cross-section view of a second ammunition roundaccording to principles of the invention.

FIG. 7 is a semi-schematic cut-away view of the round of FIG. 6 in thechamber of the tool with a spent round advanced tandemly ahead.

FIG. 8 shows the round and spent round of FIG. 7 shortly after the roundis fired. Like reference numbers and designations in the variousdrawings indicate like elements.

DETAILED DESCRIPTION

The term “ammunition” “round of ammunition”, “ammunition cartridge” andthe like are commonly associated with a self contained combination of aprojectile and propellant, typically with a case for containing thepropellant and holding the projectile and a primer for igniting thepropellant. When typical ammunition is utilized, the propellant chargeof a given round expels the projectile of that round and the spent caseis then extracted and replaced with a fresh round. For convenience,terms such as “round” or “cartridge” may be utilized to describe theammunition of the present invention, even though the rounds do notprovide the projectile and propellant for a given firing but, rather,the propellant for one firing and the projectile for the next

FIG. 1 shows a projectile cartridge 20 including a case 22, a wad 24, apropellant charge 26, and a primer 28. In the prototype embodiment, thecase is unitarily formed of machined zinc, although cast zinc ispreferred for production, and is symmetric about a central longitudinalaxis 500. Other metals, including cast and wrought metals, may beemployed. The case extends along the axis 500 from a head 30 at an aftend to a mouth 32 at fore end. The head has fore and aft surfaces 34 and36. A largely cylindrical primer pocket surface 38 extends forward fromthe aft surface 36 and terminates at a substantially annular basesurface 40. The base surface and primer pocket surface define a primerpocket having a diameter effective to accommodate the primer 28 in apress fit relation, a fore end of the primer abutting the surface 40 andan aft end substantially flush with the aft surface 36. A cylindricalflash hole surface 42 extends forward from the base surface 40 to thefore surface 34 to define a flash hole or venting between the primerpocket and the case interior.

The head includes an extractor/retention groove 50 which separates a rimportion 52 of the head from a web portion 54 of the head and a case body56. The body has an interior surface 58 which merges with the foresurface 34 of the head to form the case interior surface. An exteriorlateral surface 60 of the head and body forms a substantial portion ofthe case exterior surface.

Internally, the case interior is divided into two volumes 66, 68 by thewad 24: an aft volume or powder (propellant) chamber 66 between the foresurface 34 and an aft surface 70 of the wad; and a forward volume 68ahead of a fore surface 72 of the wad. With the exception of variousrelieved areas identified below, the surface 60 is substantiallycylindrical, having a diameter D. Along a major portion of the powderchamber, the interior surface 58 has a diameter D_(PC). Along a majorportion of the forward volume 68, the interior surface has a diameterD_(F) which is preferably greater than D_(PC) so that the wall thicknessof the body is smaller along the forward volume than along the powderchamber.

To secure the wad 24 within the case, an annular internal channel orrecess 80 in the body 56 receives an annular projection 82 of the wad.Cylindrical surfaces 84A and 84B on fore and aft sides of the projection82 engage the surface 58 to provide a seal between the wad and the case.Immediately aft of the surface 84B, the case includes an annularshoulder 86 which divides the portions having respective diameters ofD_(F) and D_(PC).

Ahead of the extractor groove 50, the exterior lateral surface 60 has anuninterrupted cylindrical portion 87. Ahead of the uninterrupted portionare a series of grooved portions (grooves) and ungrooved portions(ribs/lands) extending over a total length L₁. In the illustratedembodiment, the grooves 88 each have a length L_(G) while the ribs 89each have a length L_(R) which are of similar magnitude. The groovedepth is advantageously smaller than these lengths. At the fore end ofthe case, the exterior and interior surfaces are chamfered at respectiveangles θ₀ and θ₁ with a flat annular rim 94 therebetween at the casemouth defining frustoconical exterior and interior surface portions 90and 92.

The preferred primer is a conventional No. 209 shotshell primer orequivalent which includes a forward-facing primer cup having a generallycylindrical sidewall 104 and a web 106 spanning the sidewall and formingan aft end of the primer cup. The primer further includes an aft-facingbattery cup having a generally cylindrical sidewall 108 and a web 110spanning the sidewall at the forward end thereof to define a forward endof the battery cup and primer. The primer cup is press fit within thebattery cup adjacent the aft end thereof thus closing the otherwise openaft end. The battery cup is press fit within the head 30 engaging theprimer pocket surface 38. Proximate a rim at its aft end, the sidewall108 is flared outward.

The primer cup contains a primer charge 112 which may be covered by afoil or other layer and may preferably have a lead-free, dinol-basedcomposition. An aft-facing anvil 114 has a base held by the battery cupand a tip extending centrally into the primer cup proximate the primercharge. A circular flash hole 116 is located centrally within the web110 to provide flash venting extending from the interior of the batterycup to the powder chamber 66. When the primer cup is struck via a firingpin, forward deformation of the web 106 causes the primer charge toimpact the anvil tip igniting the primer charge. The ignited primercharge is vented through the flash hole 116 to ignite the propellant 26.In the exemplary embodiment, the flash hole 116 is a single circularaperture having a diameter roughly equal to or in excess of the 0.095inch (0.24 cm) diameter typical in a No. 209 shotshell primer. In theexemplary embodiment, the base of the anvil has a forward-facingconcavity overarching the flash hole. In the exemplary embodiment, theprimer has an overall length of about 0.3 inch (0.76 cm) and the batterycup sidewall outer surface has a diameter about 0.24-0.25 inch(0.612-0.635 cm) and preferably of about 0.241-0.245 inch (0.612-0.622cm) along a major portion surrounding the primer cup. The flaring of theaft end of the battery cup produces a local diameter of about 0.3-0.32inches (0.76-0.81 cm). Specifically, a forward portion of the batterycup extending along a length of about 0.15-0.16 inch (0.38-0.41 cm) hasan predominate external diameter of about 0.241 inch (0.612 cm). Thebattery cup, having a generally uniform wall thickness of about 0.02inch (0.051 cm) expands slightly behind the forward section to form apocket for receiving the primer cup. In this area surrounding the primercup, the battery cup has a predominate external diameter of about 0.245inch (0.622 cm) until flaring outward at the aft end.

FIG. 2 schematically illustrates a tool 200 for discharging theinventive ammunition. The tool has a barrel 202 extending along acentral longitudinal axis coincident with the projectile axis 500 from abreech end 204 to a muzzle 206. The barrel bore 208 includes rifling 210extending from a location ahead of the breech to the muzzle. A chamberarea 211 extends forward from the breech end. A bolt 212 is shown in aclosed position at the breech and carries a firing pin 214 and aretention/extraction member 216. FIG. 2 also shows a spent case 22′positioned in the chamber. The member 216 extends into the extractorgroove of the case 22′ and its aft surface engages the aft surface ofthe extractor groove to prevent forward movement of the spent case.

To load a fresh round, the member 216 is withdrawn from the extractorgroove, decoupling the spent case from the bolt, and the bolt iswithdrawn rearward to an open position (not shown). A fresh round 20 isthen fed behind the chamber and driven into the chamber by the bolt 212.A variety of known feed mechanisms may be utilized including variousactions and magazines. The insertion of the round 20 into the chamberbrings the forward rim 94 of the round into contact with the aft surface36 of the head of the spent case 22′. The insertion thus drives thespent case from its former chambered or “firing” position of FIG. 2 to asecond, “projectile,” position of FIG. 3. In the projectile position,the mouth of the spent case is advantageously very close to the aft endof the rifling. In the exemplary embodiment, each land of the riflingincludes a bevel 220 at its aft end which provides a transition from thebarrel diameter D_(G) along the chamber and grooves and D_(L) along theremaining portion of the lands. In the illustrated embodiment, thesebevel surfaces are located adjacent the chamfered surface portion 90 ofthe spent case in the projectile (FIG. 3).

With the member 216 engaged to the round 20, the pin 214 carried withinthe bolt 212 is driven forward and strikes the aft surface of the web106 of the primer cup. The engagement between the member 216 and theround 20 prevents the firing pin impact from driving the round 20forward without igniting the primer. The impact deforms the web forwardand drives the primer charge against the anvil, igniting the primercharge. Hot combustion gases and flames from the burning primer arevented through the flash holes of the battery cup and case and into thepropellant chamber 66 whereupon they ignite the propellant. Combustiongases generated by the burning propellant raise the pressure within thepropellant chamber sufficiently to drive the wad 24 out of engagementwith the channel 80, driving the wad through the forward volume 68toward the spent case (FIG. 4).

The wad 24 is driven into engagement with the aft surface 36 of the headof the spent case. Pressure from the combustion gases compress the wadagainst the spent case. Under such pressure, the wad deforms radiallyoutward so that its circumferential perimeter bears against andobturates the barrel to prevent flow of combustion gas ahead of the wadand thus around and ahead of the spent case/projectile. Expandingcombustion gases then propel the wad 24 and spent case/projectile downthe barrel (FIG. 5) and expel them from the muzzle. An additional roleof the wad may be to shield the primer cup of the spent case/projectilefrom the combustion gases. Otherwise, the primer cup might not be ableto withstand the pressure and could rupture, allowing the combustiongases to flow into the spent case/projectile and, thereby, reduce thenet force applied to the spent case/projectile.

The process may then be repeated. Optionally, if no spent case isinitially present, an unspent round may be inserted into the chamber andthen driven forward to the projectile position by a second unspent roundand launched. Additionally, if it is desired to remove a spent orunspent round from the chamber (such as for tool servicing or to removea misfired round), the member 216 is left in place as the bolt iswithdrawn and the case or the round ejected as with conventionalballistic tools and firearms.

An alternative method of operation involves advancing the spent casefrom the chambered position to the projectile position prior toinsertion of the next round. This can be accomplished, for example, by apiston mounted within the bolt. This mode of operation reduces theinsertion force required to insert the unspent round.

A preferred case material is zinc alloy AG40A, having nominalcomposition by weight: Cu 0.25% max; Al 3.5-4.3%; Mg 0.020-0.05%; Pb0.005% max; Cd 0.004% max; Sn 0.003% max; and balance Zn. Other alloysmay, however, be utilized. Conventional die casting techniques may beutilized. Other manufacturing techniques, e.g., semisolid casting(rheocasting or thixocasting), nucleated casting, and slush casting maybe utilized.

Conventional eight-gauge industrial ballistic tools have a bore diameter(groove-to-groove if rifled) of about 0.830+0.05 in. (2.11+0.13 cm). An8-gauge version of the present ammunition might risk accidental attemptsto use conventional ammunition in a tool configured for the inventiveround or vice versa Also, such a size would present difficulties inproviding the desired 3 oz. (85 g) case weight. Accordingly, the case isdimensioned for use with a barrel having significantly larger land andgroove diameters. With such a barrel, the presently preferredland-to-land diameter is 0.946 in. (2.403 cm) while the preferredgroove-to-groove diameter is 0.958 in. (2.433 cm). These largerdimensions allow the case to meet the weight goal while havingappropriate wall thickness, powder chamber volume, and volume ahead ofthe wad. The case diameter also defeats attempts to use the preferredinventive ammunition in conventional tools and vice versa. For suchbarrel dimensions, a particularly preferred case diameter D is0.95-0.958 in. (2.428-2.433 cm). This provides the maximum case diameteralong the uninterrupted portion 87 and along the ribs 89. This diameteris effective to allow the associated portions to be engraved by therifling to induce spin and to obturate with the remaining bore surface.In the absence of the grooves 88, the drag forces between the barrel andcase/projectile would be excessive, causing loss of muzzle velocity, andundue barrel wear and heating. The rounds, however, may also be utilizedwith smoothbore tools with or without rifled extensions.

A number of factors go into the selection of the geometry and dimensionsof the grooves and ribs. The greater the total length of the relievedareas (and thus the lesser the areas at or substantially at the diameterD), the lower the frictional drag from engagement with the barrel.Because of the effect of chamber pressure, the length of any givengroove should not be so great that the chamber pressure can cause thecase body to buckle outward along such area Similarly, the length ofeach of the interspersed ribs should not be so small that the chamberpressure can cause a crushing of such ribs which would, thereby, alsodrive the grooved areas radially outward. The groove depths should besufficient for the friction reduction but not so large as to eitherweaken the body and allow the aforementioned bowing out or undulydecrease the case mass which is important for maintaining the desiredkinetic energy. These factors lead to the arrangement of ribs andgrooves over a substantial length of the case. The exemplary ribs andgrooves each have lengths of 0.050+/−0.005 in. (0.127+/−0.013 cm) andcommence at a distance of 0.625+/−0.005 in. (0.159+/−0.013 cm) from theaft extremity of the aft surface 36 and extend all the way to theexterior chamfered surface portion 90.

For the chamfered surface portions 90 and 92, particularly preferredangles θ_(O) and θ₁ are 15°+/−1° and 5°+/−0.5°. The chamfered surfaceportion 90 preferably extends along a length of at least about 0.1 in.(0.25 cm) to provide a degree of improved aerodynamics as well as tofacilitate chambering of the rounds. Such length may be affected bywhether the surface portion 90 meets a groove or a rib, a preferredlength being between about 0.125 in. (0.318 cm) and about 0.16 in.(0.406 cm). The angle θ₁ is effective to ease insertion of the wad 24through the case mouth but chosen to not unduly thin the case at themouth or unduly constrain the length of the exterior chamfered surfaceportion 90.

Additionally, in the exemplary embodiment the case rim 52 may beslightly rebated (e.g., to an exemplary rim diameter similar to thediameter of the grooves 88). The extractor/retention groove 50 is,clearly, further relieved, for example to a diameter of 0.845-0.850 in.(2.145-2.159 cm), its aft surface being substantially radial and itsfore surface being frustoconical, e.g., at a cone angle of about 45°,leaving a cylindrical portion in between of about 0.085-0.090 in.(0.216-0.219 cm) in length. An exemplary rim thickness or length is0.072-0.078 in. (0.183-0.198 cm).

The wad 24 serves to encapsulate the propellant within the powderchamber. The wad should have sufficient robustness to do this throughoutan anticipated range of handling conditions. It is also desirable thatthe wad, and its engagement to the case, be sufficiently robust to allowa moderate increase in chamber pressure when the round is fired andbefore the wad is driven forward. The wad should be sufficiently thinand, thereby, leave the forward volume 68 with a sufficient length toyield lower peak chamber pressures than would be present if the wadextended all the way between the powdered chamber and the mouth. The wadshould also be lightweight, to avoid detracting from the kinetic energyimparted to the spent case/projectile. Accordingly, the exemplary wad ismolded of a plastic material polyethylene, preferably low densitypolyethylene (LDPE) is believed to provide an advantageous combinationof strength and formability for the wad. To further reduce weightrelative to its sealing capability, the fore and aft surfaces 72 and 70are formed with a central depression, being flat nearly all the way tothe outer periphery of the wad and having a fillet-like transition tothe associated rim 73A, 73B of near vanishing thickness.

As noted above, the dimensions of the forward volume 68 are particularlyrelevant to controlling peak chamber pressure. Both volume and lengthmay be relevant parameters. The volume of the propellant chamber willlargely be constrained by the required amount of propellant. For anexemplary case having a mass of 3.0 oz. (85 g), an exemplary propellantcharge is 93 grains (6.0 g) of OBP615 BALL POWDER propellant availablefrom Olin Corporation, East Alton, Ill. under license from PrimexTechnologies, Inc., St. Petersburg, Fla. For such a charge, a propellantchamber volume in the vicinity of or somewhat greater than 0.3803 in.³(6.24 cm³) is preferred. A number of factors will ultimately influencethe desired case length, wall thickness, and thus the size of theforward volume 68. The length has an influence on aerodynamics and thewall thickness (by effecting the amount of the remainder of the weightwhich is found in the case head) influences balance. Both aerodynamicsand balance may affect ballistic performance. The case length and wallthickness also influence impact performance. A relatively long case wallmay be more likely to deform upon impact. This deformation may reducethe impact shock of the projectile, thus reducing its usefulness formany applications. The deformation may also help deflect the projectile,potentially also reducing effectiveness. With the foregoing in mind, itis believed that a thin, short sidewall is advantageous for manyindustrial applications. This maximizes the mass represented by thehead. If the sidewall is sufficiently thin to be easily deformed by theimpact, such deformation will absorb a relatively small amount ofenergy. The remaining energy of the head impacting the target will stillbe effective for the intended purpose.

The dimensions of the forward volume 68 are, however, also relevant tocontrolling peak chamber pressures. For a given projectile mass, variousdifferent muzzle velocities may be desired for various differentapplications. The different applications may entail use of differentamounts of propellant and/or propellant types (bum rates). It isbelieved that for most, if not substantially all, applications, arelatively small forward volume will be sufficient for chamber pressurecontrol and thus desirable due to the impact-enhancing advantages of theshort projectile length associated with the small forward volume. It istheorized that a forward volume having a length as little as 0.05 inchesshould be sufficient to provide chamber pressure control adequate for aballistic tool used in applications for which present eight-gauge areeffective. Thus an appropriate goal for the length of such forwardvolume would be in the vicinity of about 0.05 inch to about 0.1 inch.Depending on wall thickness, with such a relatively small forward volumethe overall case length could be in the range of about 1.5 inches toabout 1.75 inches. For such a case, the head length L_(H) and the lengthL_(W) of the flash hole surface 42 and center of the web portion 54 willboth be increased by about 0.2 inch to 0.4 inch above the exemplaryprototype dimensions of 0.50 inch and 0.195 inch respectively. Anotherenvisioned modification is an alteration of the diameter of the flashhole surface 42 from the prototype dimension of 0.10 inch. A decrease inthis diameter (e.g., toward 0.80 inch) has an advantage of concentratingmass at the head. If the diameter is too small, primer recoil mightoccur. Given the length L_(W), a significant amount of propellant may becontained within the flash hole surface 42 (which thus serves as a flashtube). A larger diameter and its associated larger amount of propellantmay lead to more rapid ignition of the main body of propellant withinthe powder chamber. Thus a smaller diameter may be advantageous if aless rapid ignition is desired, for example, to help control peakchamber pressures.

FIG. 6 shows an alternate cartridge 320 including a case 322, a cover324, a propellant charge 326 and a primer 328. Subject to the discussionbelow, various properties and dimensions of the cartridge 320 may be thesame as or similar to those of the cartridge 20 of FIG. 1. The case ispreferably a one-piece casting of zinc or a zinc-based alloy while thecover is preferably a one-molding of low density polyethylene. The casehead 330 may be similarly shaped to the head 30 of the case of FIG. 1,while features proximate the mouth 332 are formed to cooperate with thecover 324. The head has fore and aft surfaces 334 and 336. A primerpocket 338 joined at a base surface 340 to a flash hole surface 342 maybe similarly formed to that of the case of FIG. 1. In order to easemanufacturing, the flash hole may preferably have at least a slight(e.g., 1°) fore-to-aft taper. Extractor/retention groove 350, rim 352,and web 354 may be similarly formed to corresponding elements of thecase of FIG. 1. The wall thickness of the body 356 is generally greaterthan that of the case of FIG. 1, with a body interior surface being ofrelatively smaller diameter while body exterior lateral surface 360 maybe of similar diameter. A main portion of the body 356 terminates at anannular forward-facing shoulder 362. A neck 364 extends forward from theshoulder to a flange 366 having a diameter intermediate those of theneck and body main portion. At its forward extremity, the flange ischamferred or bevelled both internally and externally. The body interiorsurface 358 extends continuously through the flange, neck and main bodyportion having a fore-to-aft taper. The body interior surface 358cooperates with the flash hole surface 342 and primer pocket surface 338to form a central longitudinal channel extending through the case.

The cover 324 includes an inwardly-directed flange 368 at an aft rim369. An inwardly-facing surface 370 defining a central aperture in thecover flange 368 has a diameter smaller than a diameter of an externalcylindrical surface of the case flange 366. This permits the coverflange 368 to be captured between the case flange 366 and the shoulder362. In the exemplary embodiment, there is a radial gap or clearancebetween the case flange 366 and the cover interior surface 372 so thatthe aft surface or underside of the case flange 366 covers and contactsonly an inboard portion of a forward facing surface of the cover flange368. In its installed condition, the cover cooperates with the bodyinterior surface to define a powder chamber containing the charge 326.In the exemplary embodiment, the powder chamber has substantially morevolume than is necessary to contain the charge. The charge may beunrestrained within this additional space or an additional member suchas a wad may be located within the cover to further confine the charge.

At an intermediate position along the length of the cover, the cover islocally weakened such as by provision of an annular channel 374 in theinterior surface 372. The channel 374 divides fore and aft portions 375Aand 375B of the cover 324. An exemplary channel 374 is formed as a fullradius channel having a depth half its longitudinal extent. The coverexterior surface 376 is generally cylindrical from the rim 369 forwardto a rounded transition (e.g., I/O radius of 0.25 in.(0.64 cm)) to aflattened front end 378.

The case exterior surface 360 is advantageously provided with analternating series of grooves 388 and ribs 389.

Dimension Value (in. (cm) unless noted) Rim diameter 0.937 − 0.003(2.380 − 0.008) Rim length 0.075 − 0.003 (0.191 − 0.008) Extractorgroove base diameter 0.850 − 0.005 (2.16 − 0.013) Extractor groove baselength 0.085 + 0.005 (0.216 + 0.013) Neck length 0.100 + 0.005 (0.254 +0.013) Neck diameter 0.500 +/− 0.003 (1.27 +/− 0.01) Case flange length0.250 +/− 0.005 (0.635 +/− 0.013) Case flange diameter 0.588 +/− 0.003(1.494 +/− 0.008) Case flange I/O chamber 0.02 (0.05) × 45° Head foresurface diameter 0.240 +/− 0.005 (0.610 +/− 0.013) Case interior taper2° +/− 10′ Rib and groove pitch 0.100 (0.254) Rib length 0.032 +/− 0.005(0.081 +/− 0.013) Maximum case (rib) diameter 0.955 − 0.003 (2.426 −0.008) Groove diameter 0.944 − 0.004 (2.395 − 0.010) Overall length2.938 (7.463) nominal Case length 1.363 +/− 0.003 (3.462 +/− 0.008)Cover length 1.825 +/− 0.050 (4.636 +/− 0.127) Cover outer diameter0.943 +/− 0.005 (2.395 +/− 0.013) Cover principal inner diameter 0.780+/− 0.010 (1.981 +/− 0.254) Cover flange thickness 0.100 +/− 0.005(0.254 +/− 0.013) Cover flange inner diameter 0.500 +/− 0.003 (1.270 +/−0.008) Cover groove depth 0.040 (0.102) Flash hole length 0.50 (1.27)Flash hole diameter 0.10 (0.25) Case mass 3.00 +/− 0.01 oz. (85.0 +/−0.3 g) Cover mass 6.5 +/− 0.1 g Propellant charge 90 grains (5.8 g)

Relative to the cartridge 20, the foregoing dimensions provide thecartridge 320 with both a smaller maximum diameter and a smaller totallength of material at that maximum diameter. This reduces barrel wearand the required insertion force to chamber a round and drive a spentround forward into the projectile position.

Various parameters of use of the cartridge of FIG. 6 may be similar tothat of the cartridge of FIG. 1 and are not repeated in detail. However,FIG. 7 shows an unfired cartridge 320 chambered behind a spent cartridge320′ analogous to the illustration of FIG. 3. The spent cartridgecomprises the case, spent primer, and aft portion of the cover of thepreviously-fired round. When the cartridge 320 is fired, pressureincreases within its cover. The pressure increase is effective torupture the cover at the channel 374 separating the fore cover portionfrom the aft cover portion (FIG. 8) and permitting expanding gas todrive the fore portion along with the spent cartridge ahead down thebarrel. The fore cover portion can provide a significant degree ofobturation, significantly preventing combustion gasses from passingaround the spent case/projectile. This, in large part, facilitates arelatively low maximum case diameter and a relatively low portion ofmaterial at that maximum diameter by reducing the need for thecase/projectile to obturate itself.

Additionally, the aft cover portion helps prevent combustion gasses fromflowing back around the case being fired. The presence of the radial gapbetween the case flange 366 and cover interior surface 372 permitscombustion gas pressure to act on the adjacent portion of the foresurface of the cover flange 368 pressing the aft surface thereof intofirmer engagement with the case shoulder surface 362 to resistinfiltration of combustion gasses between the cover and case and therebyaround the case.

Because of the possibility of additional wadding, encapsulatingmaterial, or the like, and to avoid any confusion regarding the scope ofthe claims, as such items are argued as being “projectiles” variousclaims may identify a lack of a substantial or effective projectile bydefining a maximum mass of any item which could be asserted as aprojectile. Where dimensions are given in both English and metric units,the English units are the original value and the metric units are aconversion.

One or more embodiments of the present invention have been described.Nevertheless, it will be understood that various modifications may bemade without departing from the spirit and scope of the invention. Forexample, although various preferred dimensions have been identified,there remains flexibility in choosing the particular dimensions of aparticular cartridge. If compatibility with the preferred cartridge (orwith any particular cartridge) is desired, then flexibility in certainof the dimensions may be highly limited. Accordingly, other the scope ofthe following claims.

What is claimed is:
 1. A ammunition in combination with a dischargingapparatus for firing such ammunition wherein: the discharging apparatuscomprises: a chamber for receiving the ammunition; a muzzle; and abarrel between the chamber and the muzzle; and the ammunition extendsfrom a rear end to a front end and comprises: a metallic case that:extends aft-to-fore from a base at the ammunition rear end to a mouth;has interior and exterior surfaces; has a central longitudinal channelextending forward from a primer pocket portion at the base to a foreportion proximate the mouth; and has a length and diameter effective tobe initially accommodated within the chamber and then, after firing, tobe driven forward into the barrel and discharged therefrom by suchfiring of a subsequent similar ammunition; a cover formed of polymericresin and extending from a rear rim to a front end at the ammunitionfront end and having a mass not in excess of a mass of the case andhaving interior and exterior surfaces; a primer mounted within theprimer pocket; and a propellant charge confined within a volume at leastpartially defined by the central longitudinal channel and the coverinterior surface.
 2. Ammunition in combination with a dischargingapparatus for firing such ammunition wherein: the discharging apparatuscomprises: a chamber for receiving the ammunition; a muzzle; and abarrel between the chamber and the muzzle; and the ammunition extendsfrom a rear end to a front end and comprises: a metallic case thatextends aft-to-fore from a base at the ammunition rear end to a mouthand has interior and exterior surfaces, the metallic case having a caselength and diameter effective to be initially accommodated within thechamber and then, after firing, to be driven forward into the barrel anddischarged therefrom by such firing of a subsequent similar ammunition;a cover formed of polymeric resin and extending from a rear rim to afront end at the ammunition front end and having a cover length greaterthan the case length having a mass not in excess of a mass of the caseand having interior and exterior surfaces; and a propellant chargeconfined within a volume at least partially defined by a combination ofsaid case and said cover.
 3. The combination of claim 2 wherein: thecover consists essentially of injection molded high densitypolyethylene; and the case consists essentially of die cast zinc or zincalloy.
 4. Ammunition in combination with a discharging apparatus forfiring such ammunition wherein: the discharging apparatus comprises: achamber for receiving the ammunition; a muzzle; and a barrel between thechamber and the muzzle; and the ammunition extends from a rear end to afront end and comprises: a metallic case that extends aft-to-fore from abase at the ammunition rear end to a mouth and has interior and exteriorsurfaces, the metallic case having a length and diameter effective to beinitially accommodated within the chamber and then, after firing, to bedriven forward into the barrel and discharged therefrom by such firingof a subsequent similar ammunition; a cover formed of polymeric resinand extending from a rear rim to a front end at the ammunition front endand having a mass not in excess of a mass of the case and havinginterior and exterior surfaces, the cover interior surface having acircumferential recess forward of the case and effective to locallyweaken the cover sufficiently to permit internal pressure within thecover to sever a portion ahead of the recess from a portion behind therecess while the portion behind remains attached to the case when theammunition is fired; and a propellant charge confined within a volume atleast partially defined by a combination of said case and said cover. 5.The combination of claim 4 wherein the circumferential recess: has alongitudinal extent of between 1 mm and 5 mm; and locally thins thecover to a minimum thickness of between 0.6 mm and 1.4 mm from anadjacent thickness of between 1.6 mm and 2.6 mm.
 6. In an ammunitionround for use with a discharging apparatus that includes a chamber forreceiving the ammunition, a muzzle and a barrel between the chamber andthe muzzle, wherein the case of one round fired by the apparatus servesas a projectile expelled by ignition of the propellant charge containedwithin the case of the next round, the improvement wherein: the case isformed of a cast zinc or a cast zinc-based alloy that extendsaft-to-fore from a base to a mouth and has interior and exteriorsurfaces; the primer is mounted in the case; and a member cooperateswith the case to enclose the propellant charge the case exterior surfacehas a plurality of interspersed circumferential grooves and ribs, theribs having a diameter effective to engage rifling of the barrel.
 7. Theammunition of claim 6 wherein there are at least eight said groovesoccupying a total of at least about 25% of a length of the case.
 8. Theammunition of claim 6 wherein the plurality of grooves have widths ofbetween 0.9 mm and 1.8 mm peak depths of between 0.08 mm and 0.30 mmfrom a maximum case diameter and, along with said ribs extend along atleast 70% of the case length.
 9. The ammunition of claim 8 wherein saidpeak depths are between 0.13 mm and 0.23 mm and said interspersedungrooved areas have diameters within 0.05 mm of the maximum casediameter.
 10. The ammunition of claim 8 having dimensions effective forprojection from an industrial ballistic tool barrel having rifling witha land-to-land diameter which is 0.943-0.950 in and a grove-to-groovediameter which is 0.954-0.960 in.
 11. The ammunition of claim 8 whereinthe case exterior surface has circumferential extractor groove having adepth of at least 1 mm and separated by no more than 2 mm from an aftextremity of the case.
 12. The ammunition of claim 6 wherein the memberis a cap extending from a rear rim to a front end and having a rearportion encircling a fore portion of the case.
 13. The ammunition ofclaim 12 wherein: the cap is formed of a resinous polymer; the case foreportion includes a flange having an external flange diameter; the caprear portion includes an inwardly directed part aft of the flange andhaving an internal diameter less than the flange diameter so as tocooperate with the flange to resist forward translation of the caprelative to the flange; and a cap length is between 100% and 300% of acase length.
 14. The ammunition of claim 13 wherein: there is a firstradial clearance of at least 1.0 mm between the flange and the cap; andthere is a second radial clearance of between interference fit and 0.5mm between the cap inwardly directed part and a neck portion of the caseaft of the flange.
 15. The ammunition of claim 6 wherein the member is acover having a reduced thickness portion effective so that upon thefiring of the propellant charge of a given round a first portion of thecover ahead of the reduced thickness portion will be severed form asecond portion aft of the reduced thickness portion and travel behindthe spent case of the prior ammunition round.
 16. The ammunition ofclaim 6 wherein the primer is a #209 primer press fit within a headportion of the cast zinc or cast zinc-based alloy case.